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flattracker 08-19-2020 11:50 PM

The Conversion of my 86 Crown Supercoach
This is the documenting of the Conversion of my Crown Tandem Axle School Bus to a Motor Home.

About me:
I am a retired Software Engineer with a thirty one year career in the aerospace industry. I also have experience in hardware and software test. Before that I served eight years in the U.S. Air force, working on Electronic Countermeasures. This is my second bus conversion.

About the bus:
It is a 1986 Crown, 39 feet in length, tandem axles, originally equipped with a Cummins Big Cam I 300 engine, an Alison HT740 automatic transmission, Rockwell differentials with a 4.10 gear ratio, and rear air ride suspension. It was last in service in King City, Ca.

TJones 08-20-2020 12:10 AM

Welcome! Sounds like a nice bus. I love the classic look of Crowns. Looking forward to your build.


Native 08-20-2020 02:35 AM

Oh goody ... a crown conversion build thread I can read daily ... from the ground up.
Welcome to the site.

flattracker 08-21-2020 02:09 AM

The Conversion of my 86 Crown Supercoach
I have been approaching my conversion project with an engineering point of view, so some of what I document will be somewhat detailed.

An old racing buddy of mine found the bus in Salinas Ca. in the hands of a private party and told me about it. I purchased the bus for $3000. My friend serviced it for me and removed the seats as my insurance company would not cover the bus until I produced a picture of the interior with no seats. With insurance coverage secured, with title in hand I purchased a trip permit at the Oregon DMV. My brother and I drove about 500 miles to Salinas, installed a queen size bed in the rear of the bus, a bathroom vanity with a counter top attached, and a three burner cook top with 5 gallon propane supply. Now configured as a motor home per California and Oregon requirements, I drove it home., took a trip to DMV and passed the inspection by DMV to verify it met Oregon requirements. I now had an Oregon legal motorhome.
I had made arrangements to keep the bus in a storage yard at Bly, Ore. so I now had the start of my project.

The design process:
I made a list of the features I wanted in this motor home, basically a list of requirements for the new motor home, some detailed some general (the engineer part of me). The requirements list changed when components I wanted became available.
Making a wish list of what you want in your conversion allows you to price out what you wish to put in it. It also will make clearer to you how much work you will have to do to complete your project. Since I have already converted a Crown to a motor home before I knew what I was getting into and kind of how to do it.

In my next post I will provide my requirements list.

flattracker 08-22-2020 01:27 AM

The conversion of my 86 Crown Supercoach
2 Attachment(s)
Tonight's post provides some pictures of my Crown inside and out as well as my requirements that describe how the conversion will be constructed and what items will be included.

My approach to how and what goes into my conversion is designed to suit my wife and I (and our cats) and others would find different priorities. That being said certainly one could change their own design to suit themselves better (more beds, different seating, kitchen size, etc).

Keep in mind that designing a motor home conversion is a task and to complete that task, one has to define that task first (much like problem solving), so listed below is a set of major requirements for the finished project.

Our project has the following general requirements:

1) Sleeps only a couple (two) in one bed, which must be comfortable.
2) I must have a full bathroom, toilet, shower, sink, with doors for privacy.
3) It must have a full kitchen, Fridge, gas range with oven, two tub sink, and counter space.
4) It must have a front room with seating, dining table, TV and stereo system.
5) It must have closet space for two, storage for dishes, food, utensils, cleaning products, etc.
6) It must have adequate heating and cooling.
7) It must be constructed so that any part of heating, cooling, plumbing, electrical can be repaired or replaced by one person (me).
8) It must be able to be used in Winter without failure from freezing.
9) It must have solar, generator, and outside power capabilities.
10) It must have a washer/dryer (because the wife wants it to).
11) The design must follow the K.I.S.S principle.
12) It must be made so that it won’t squeak or rattle or vibrate going down the road.
13) No fresh water plumbing underneath the floor.
14) It will use Propane for cooking and heating.
15) It will be insulated to increase efficiency for heating and cooling.
16) It must be made SAFE to use for driver and passengers.
17) The Wife must be consulted for layout and appearance issue and reasonable compromise reached for these things.
18) It must be easy to use and operate.
19) No structural changes to the bus. (don’t add or move entry doors, cut or modify frame)

A lot of the above items are common sense.

Some of the following design details I have derived from the above requirements:

Power system:

1) Solar Power – The solar system shall use flexible solar panels mounted to the roof. The solar array shall be capable of generating 1 Kw on a bright day. I am using 100 watt panels. The power generated by the array will be passed through a charge controller to a battery bank located in the trunk of the bus (Most Crowns have a large trunk located at the rear of the bus).
2) The battery bank shall be capable of storing 1000 KwHr of energy.
3) There shall be a 65 Amp battery charging system that will, in addition to the solar array, charge the batteries when the bus is using shore or generator power.
4) The DC power from the batteries (12VDC) shall be available to a 3Kw true sine wave inverter, and to various 12VDC circuits.
5) All 12 VDC circuits shall be protected through circuit breakers in a central panel.
6) All 120 VAC circuits shall be protected through AC circuit breakers in a central panel
7) The 65 Amp battery charging system will only operate when external or generator power is being used.
8) The washer/dryer will only operate when using external or generator power.
9) The AC power source switching (External/Generator/Internal) shall be mutually exclusive, meaning only one at a time is available.
10) When connecting to external power, the system shall be capable of accepting 240 VAC and distributing such power to 120 VAC circuits.
11) When using Generator power the system will accept 240 VAC and distribute such power to 120 VAC circuits through standard electrical boxes with circuit breakers.
12) When using internal power, the system will accept 120 VAC from the inverter and distribute such power to 120 VAC circuits.
13) The 12 VDC circuits will have power available regardless of which power source is selected.
14) The power system shall have voltage/current/frequency monitoring at all times, in all power source modes.
15) The power system shall be capable of complete shutdown by use of switching.
16) The Crown bus electrical system shall be isolated from the motor home electrical system, except when cross-connected through a battery switch for emergency use to start the bus engine if the Crown bus batteries become unable to start the bus.
17) A second 250 Amp alternator shall be installed on and rotated by the bus engine. This alternator shall be connected to provide additional charging of the trunk mounted battery bank.
18) The second alternator shall be capable of cross connection to the bus batteries for emergency charging if the bus batteries become excessively discharged.
19) The generator shall be an Onan 6.5 DKD diesel generator, capable of 6.5Kw at 240 VAC.
20) The generator shall have a 20 gallon fuel tank mounted forward of the engine compartment.
21) There shall be a semi-automated fuel transfer system to transfer fuel from the main engine fuel system to the generator fuel tank. The fuel transfer system will stop fuel transfer when the generator fuel tank gets nearly full or when the main fuel tank get down to 25% full.
22) The generator fuel tank shall have a manual fuel filler capable of being fueled using a standard fuel pump as found at a gas station or truck stop.
22) There will be a 20 gallon fuel tank mounted in the trunk, capable of transferring fuel to the main fuel tank through the main tank fuel filler. This transfer shall be manually operated.


1) The kitchen shall have a Suburban 3 burner range/oven operated using Propane.
2) The kitchen shall have a 10 Cubic foot refrigerator made by xxxx, operating from 120 VAC.
3) The kitchen shall have a two tub stainless steel sink xxx X xxx X xxx inches. The faucet shall supply hot/cold water through one spout and a sprayer.
4) The counter tops shall be acacia wood butcher block 1 ˝ “ thick and 25 inches deep.
5) Under the sink/counter shall be a 40 gallon fresh water storage tank. This tank shall be filled from a standard outside RV water connection through a manually operated valve.
6) The outside water supply shall be passed through a pressure regulator and a filter.
7) When connected to outside water, the water shall be distributed through the bus using outside water pressure.
8) When water source is internal the water in the storage tank shall be distributed by a 3 GPM electrical pump operated on 12 VDC.
9) The kitchen walls will be covered with sheet aluminum for ease of cleaning and fire safety.


1) The toilet and bathroom sink shall be enclosed in a “water closet”, installed on the right side of the bus. The “water closet” walls shall be covered with FRP.
2) The Shower shall be installed on the left side of the bus and shall be 30” x 30”. The shower will have plywood walls covered by FRP.
3) The water supply for the shower shall be passed overhead in the transition between the bathroom and utility cabinets/closet to the rear.


1) The bedroom shall have a custom built queen sized bed mounted to the floor. The pedestal under the bed shall have two drawers installed for storage.
2) The bedroom shall have access through the emergency door for egress if needed.
3) The back wall of the bus shall be enclosed to provide storage cabinets, shelves and electrical power.

Front room:

1) The front room shall have three sets of reclining “tour bus” seats. Two of the sets will be mounted facing each other, with a dining table mounted between to provide a booth for dining. The booth will be mounted on the left side of the bus. The third seat will be mounted to the right side wall of the bus in a forward position. The third seat will be a single modified tour bus seat with cup holder, phone holder, and USB charging connections

2) The front room will have a 55” 4K TV mounted on the right wall across from the booth. The TV will be mounted to a lift mechanism to raise the TV up for viewing and lower it when not in use.

3) The front room will have a stereo system with:
a) Two 350 watt per channel amplifiers.
b) Peavey graphic equalizer
c) Preamp/FM/Tuner
d) Power control panel
e) 300 watt subwoofer amplifier
f) 15” subwoofer speaker/cabinet
g) Two Carvin speakers (2’ x 3’ cabinets)
4) The stereo system will be connected to a Raspberry Pi 4 single board computer using the Libre Elec /KODI software to play movies/music and to the TV through HDMI interface for playing movies.


1) A 40,000 btu suburban propane burning ducted forced air furnace shall be installed underneath the gas range/oven. Ducting will provide forced air heat to the front room, kitchen, and the bathroom. The furnace will operate using 12 VDC and be thermostatically controlled. The intake air to and exhaust from the furnace will be through the left wall of the bus.
2) A 16,000 btu suburban propane burning unducted forced air furnace shall be installed on the left side of the bus in the bedroom. The furnace will operate on 12 VDC and be thermostatically controlled. The intake air to and exhaust from the furnace will be through the left wall of the bus.
3) The original factory installed heating system in the front of the bus will be retained.


1) There will be two 13,000 btu coleman roof mounted air conditioners installed, one over the front room and one over the bedroom. They will operate on 120 VAC.

Wall/Cabinet Framing:

1) All walls and cabinets and counters, tank mounts will be constructed using UniStrut.
2) Where needed the UniStrut will be welded using MIG.
3) Rivnuts will be incorporated where attaching framing to bus ceiling where needed.

Generator mounting:

The generator will be mounted in the spare tire well of the bus, as well as its fuel tank. The generator fuel tank can be filled using fuel transfer from the main tank or through manual filling through conventional car type filler inside generator access panel.

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Native 08-22-2020 03:28 AM

It is refreshing to see a build thread that actually has a plan.


Originally Posted by flattracker (Post 401856)
2) The battery bank shall be capable of storing 1000 KwHr of energy.

Did you really mean 1000 KwHr? That is 1 MwHr of storage.

flattracker 08-22-2020 05:11 AM

It was misstated on the battery capacity. I believe I meant 1000 amp hours. thanks for catching it

TJones 08-22-2020 09:13 AM

Great detailed plan. Specified like a true engineer.:thumb: I have a BS in mechanical engineering that I ended up using to be a ski instructor and owning a landscape company.:biggrin:


flattracker 08-22-2020 10:47 PM

The Conversion of my 86 Crown Supercoach
With my new to me 1986 Crown bus, a place to keep it and permission to work on the conversion I was ready for the project.
I didn't have any of the items to install in the bus yet, and while I had experience with converting my 1981 Crown, It was the thirty five foot two axle version, and is equipped with the Detroit 671 diesel with an Alison automatic transmission. The new Crown being equipped with the tandem axles and the Cummins Big Cam III 300 presented a different "canvas" for me. While the 81 Crown was reliable, it is on the slow side on hills.

I began the design process that resulted in the requirements and specifications listed in the previous post. Once I determined what I wanted in the conversion, I began purchase of materials and components to install in the bus. Most items I acquired through eBay.
I bears mention that my specification calls out the use of "Unistrut" also known as "Hardystrut" and a couple other names. It is a steel product, a "U" shaped channel with the open ends curled around. I comes in ten foot lengths, punched with holes or not. You might see it in a warehouse or an auto parts store used to construct shelving. It is an incredibly strong product, plated for rust resistance, and is weldable. I used it on my first conversion, and will use it on this one.

Over the rest of last Summer, last fall and Winter, I did the layout for each room, the detailed design for walls, counters and appliances, while acquiring the items. None of my design work was first cut success, rather most having multiple re-design efforts. In my case I used a spiral notebook to document the design, and calculations need to refine the design. All this may not be exiting reading but I found that doing this first has saved me much aggravation.

In the next post I will talk about a problem that almost ended the project before it really started.

flattracker 08-22-2020 11:37 PM

The conversion of my 86 Crown Supercoach
In this post, I talk about an expensive failure that almost ended the project before I started it.
Back in January I went to the storage yard in Bly, and started the bus as I had been doing on a semi regular basis. It didn't run right and would not idle. I first attributed the problem to cold temperatures. It had oil pressure.
In March I attempted to start the bus, and found it would not even turn over. I had the starter rebuilt (about $250), no help. I replaced the batteries, still no help (about $400).
I called a mobile truck mechanic who troubleshot the problem and determined that one of the main bearings were spun, meaning that the bearing was welded to the crankshaft and the bearing had turned in the block, damaging it.
Such failures do not mean that the engine is ruined but to repair the damage requires line boring of the block and replacement of the crankshaft. This also requires complete stripping of the block. This is very expensive.
Fortunately the mechanic knew of a guy that has a tow service for big trucks and that he had a Cummins Big Cam engine he might sell. I went and saw the potential donor engine, it started up fine, ran OK (it was installed in an old "Pete" tow truck), so I was able to purchase that engine and got a big price break on towing as a package deal.
The engine cost was $3700 and the tow $350, going 60 miles to Klamath falls, a great deal.
The mobile mechanic also had a shop, where the Crown would be repaired.
The replacement project entailed removal of the engine and transmission, stripping the new engine to a long block, replacing the rod and main bearings (a good idea since the oil pan had to come off). The fuel pump on the replacement engine was sketchy so the fuel pump from the Crown's engine was gone through and re-calibrated for a Cummins Big Cam 400. The original engine was rated at 300 HP and the replacement engine is rated for 400 HP. As the original bus engine was a Big Cam III with mechanical valve timing (MVT) and the replacement engine a Big Cam I with fixed valve timing, all external components from the original engine were installed on the replacement engine. It turns out that the differences between the Cummins 300 and the 400 are the fuel injectors and the fuel pump are different. The difference between the injectors is slight and the fuel pump can be re-calibrated for 400 HP.
There are improvements that came with the Big Cam II and Big Cam III engines and all of these except the MVT (which is known to be problematic) ended up in the engine. Of note, the compressor used in the Crowns with a Cummins Big Cam are special, and the regular Cummins compressor cannot be used.
After some initial problems were worked out, I drove the bus back to Bly. One thing I noticed immediately was the extra horsepower. This bus was a rocketship.

Fixing a configuration problem with the Crown.
This bus was a school bus, made to stop every few blocks and either pick up or drop off kids, and usually did need to got faster than 50 MPH.
The Rockwell differentials in this bus came with a 4.10 gear ratio, great for school bus usage or drage racers, but not good for interstates, especially in states like Nevada, Idaho, Utah, Colorado, Montana, etc. where the speed limit is 80 MPH. With a 4.10 gear ratio the engine reaches 2100 RPM at 63 MPH. I don't want to be THE GUY going 60 MPH in an 80 MPH speed zone. Also if running a Cummins at 2100 (redline) isn't great for it and fuel economy is NOT good.
My solution:
The Rockwell differential used by Crown are available with different ring and pinion gears, with the tallest gear ratio being 3.42. I had the same shop remove and replace the "pumpkin" in each differential with rebuilt units with the 3.42 gear ratio. Cost for this was about $6200, but worth the cost.
Ultimately the Crown ended up with a 25% increase in torque (and HP) and a 16% taller gear ratio. Top speed is calculated at about 77 MPH.

The Crown had some air system issues to fix and those will be discussed in the next post.

Crown_Guy 08-22-2020 11:50 PM

Congrats. You have a very good Crown to do a long distance build on.
I think it's the best combination of overall size and massive power to make any road trip enjoyable and drama free. For me, most of the reason for having and driving the Crown is the sublime experience of Just Driving it on the road. I have many more miles driving commercial coaches over the years but the Crowns are hands down the most fun to drive and keep you in touch with the country you're passing through and the feel of the road under you like a sports car.

Since you're a previous Crown owner I don't have to tell you how they are on the road. And that monster Cummins will make a believer out of you for sure. As much as I love my Scream'n Jimmy's I have to say that the Cummins is much quieter and easier on the ears for long hours on the road. You also don't need to thrash it and keep your foot buried in it all the time to keep your road speed up(non-turbo'd). Or watch your temp gauge on hot days and steep hills. Crowns don't usually get hot but on really hot days and steep hills a 6-71 will need to be watched and probably down-shifted to keep it cool. An extremely well engineered and well balanced cooling system for the engines installed by Crown.

The most common reason for downshifting on hills is just plain running out of torque to pull any longer in that gear. It'll drop to 1600rpm where you must downshift or risk lugging and hurting the engine. Some say to downshift at 17-1800 and keep it up close to, or on, the max governor speed at around 2200 or so. The 2-strokes demand this driving technique or you WILL do damage to them. I say you need to drive them like you're always mad at them. They love it and thrive on it.

I'm sure you'll find that Cummins won't be going slowly up hills. In fact I'd guess it only does about 63-65mph max at about 2100 rpm. I know the engine will turn as high as 2400rpm without shutting down like the 6-71 governor would....well that's the way Cummins work. So you may be getting a usable highway speed with it and the normal 4.10 rear-end gears. Very normal speeds for the originally ordered school bus operators with 4.10's was a max of about 63 at governed engine speed.


Additional edit**** I was doing my reply when you posted before I was done. Your solution of changing out the rear end gears was what I was going to mention to you......but Nevermind as Gilda used to say.

You now have one of the ultimate Road buses and it still won't notice what a hill is. I know because mine has a 300hp Big Cam III with a 10spd overdrive transmission and I rarely take it out of 10th (o.d). Good for you and you're right it's worth the cost to have that highway speed on the 80mph posted interstates.

Depending on the exact setup of your engine you may be able to cruise with it at insanely low engine speeds (for us with many 2-strokes miles under our belts). I suspect you can easily maintain about 16-1700 rpm at 65-70 or so which will not hurt the engine. My engine is rated for 1050ft/lbs at 1300 rpm and it does it too. Unless you have a Big Cam III (which I doubt it is) you may need to keep it up above 1600 or so for max torque.


More update.... I just read the WHOLE post above about the engine swap so please ignore some of the stuff I'm off about. It's not worth re-doing it. I have a mild concern about the differences in the 80 degree laid down pancake configuration used in the Crown, and that all the tricky oil return and other little internal things were done properly. You found one of them, the fuel pump is a different part number, as I found when I re-built mine. I'm told there are other deeper differences that should be heeded in order to lay one down, and I believe them. I know personally of one guy who tried what you did but did none of the appropriate modifications to lay it down and he got about 5 miles down the road before a piston flew out the side of the block due to oil starvation.

Rocketship, I'll bet, I know how mine drives and with 400 rated HP I'd only worry that I was taking a hit in fuel mileage. I plan on looking into this one day to see if I can gain anything useful. In the mean time I fly over Cajon pass with 10 or so pax and lots of onboard parts and such, at almost 65 mph in 10th over and about 1400rpm and it doesn't drop any lower, just digs in more, kind of like the Caterpillars do. Awesome setup really and a true joy on the open road.

I'd check with Cummins direct and see if you can find out all the modifications for that special engine model used in Crowns to be totally safe. I look forward to talking with you.


But that Cummins won't even slow down or show you it knows what a hill is. Torque to Die for. Try to verify exactly what the engine is. A Big Cam I, II, III, or something else. It matters due to the Big Cam III having an increased torque rating over the previous builds. The 350 is in fact an earlier 743 block and not the 855 which the Big Cams are all built on.

I have a listing of the various Crown specific Cummins model/HP engines with their torque/rpm ranges I can send you if you contact my email. That way you can begin to get a handle on what exactly is in your Crown. There's a lot of well meaning and unintentional confusion on the Cummins, and I was among those until I did some digging to sort out what I had in mine. There should be an engine serial number plate on it someplace and with that you can contact Cummins service direct and get the details for your engine. You'd be amazed at all the little things they can tell you about it that you're going to need in the future, I know I was.

The 6-71 Crown probably had the same school bus geared rear end as well so you may not see any real increase in road speed. Also I suspect the 6-71 may have only been naturally aspirated with no turbocharging. In that year range it was still an extra cost option seldom bought. It's true a 6-71 without turbo charger is typically sluggish, like 30-35 mph, up a decently steep highway grade. That's just the way they are and we all got used to it. The Turbo'd 2-strokes and series 60 4-strokes in the coaches certainly spoiled us forever with the old ways of going up hills, watching the temp gauge and downshifting to keep the engine in the torque range and circulating coolant to keep it cool.

You have an outstanding Crown with the best combination of power and never ending long distance highway driving, plus that Allison automatic makes it as easy as a car to drive so you both can enjoy the thrill of driving the Crown on the highway. Nothing else comes close to that. The air ride rear is a great feature to have since the fully sprung tandems were pretty hard riding until they got a real heavy load of bodies on board.

One thing I bet you'll find, like I am, is that those rear wheel humps are taking away from usable flat interior floor space and where to locate things. I'm still not sure how or where to place some basic items like the toilet, and how to run the plumbing without cutting any holes in the floor. That extra 5ft over the 35ft two axle Crown comes with a penalty called the second rear axle hump. It appears to be a complete wash. I think we're the ones being humped actually. Oops. Like you I don't like cutting holes and will do everything I can to not have to penetrate the existing structure as best I can. Contact me so we can compare notes.

flattracker 08-23-2020 01:37 AM

Hi Mike,
My understanding from our local Cummins expert was that other than oil pan and compressor the horizontal configuration is identical to the vertical one. I have put about 130 miles on the bus since the re-power and it still run perfect. I have and will put holes through the floor for plumbing, gas and electrical. It seems impossible to not have to do that in a conversion. I will need to cut through the side for the water heater and furnaces. I had no issues on my first crown. I like the crown in your picture.

Crown_Guy 08-23-2020 02:11 AM


Originally Posted by flattracker (Post 402001)
Hi Mike,
My understanding from our local Cummins expert was that other than oil pan and compressor the horizontal configuration is identical to the vertical one. I have put about 130 miles on the bus since the re-power and it still run perfect. I have and will put holes through the floor for plumbing, gas and electrical. It seems impossible to not have to do that in a conversion. I will need to cut through the side for the water heater and furnaces. I had no issues on my first crown. I like the crown in your picture.

Good. I'm glad you made the effort and checked into it. My problem is I have so much time and miles on the 2-strokes I haven't yet found a true Cummins "expert" I can trust and query about the Zen of Cummins engines. I definitely have that in spades when it comes to Detroits. I have one of the best guys around whenever it involves anything Detroit 2-stroke. He works on others of course but he's a master when it comes to Detroits.

My engine runs and purrs so good I haven't had any need to look around for a really good Cummins guy..yet. Except for the previously mentioned fuel pump issue, which started out as a simple slow fuel leak around the throttle input shaft, and it's silly little internal seal which is a known issue apparently. It needed to be removed and opened up to do the seal and of course while at the diesel injector shop it made no sense not to have the whole thing rebuilt and zero timed. This was when they told me I'd have to wait to rebuild my pump instead of merely getting one off the shelf because it was a different part number with several internal differences due to the horizontal configuration.

I always remembered this as well as what others have said through the years about the engineering differences to lay the engines down. I've also heard over the years it took a lot longer for Detroit Diesel to do the horizontal configuration on the 6-71's than it was for the Cummins. Which might explain the ease for the Cummins and the early Crown diesel conversions were only available with Cummins 220's then 262 turbo's. Mostly due I suspect to all the issues I've heard about with the 6-71's. Once they got the 6-71 figured out it became more popular and that's why you see so many more of them in the Crowns. Cheaper initially and back in the day much cheaper and easier for parts and labor to repair compared to the Cummins. Not so much today with all the experienced 2-stoke mechanics retiring and not being around.

You've got an outstanding Crown and have solid plans for getting the most out of it. Feel free to email me so we can swap numbers and we can keep in touch and I can answer any questions you might have and help you get in touch with other Crown owners who would like to know about you also. There's more of us every day.

I have cleaned it up some since I took that pic on picking it up. The huge black patches are gone and the paint has been buffed out to remove the oxidation, Crown used the most superior paint I've ever seen. It seems to last forever. I really haven't done much more than clean it up a little and drive it every month to keep it charged and limbered up. It awaits my attention and $$$ to really get started on it but I'm getting closer to being able to do that. I might as well try updating the avatar if I can find a good one to use. Thanks for reminding me.

flattracker 08-23-2020 11:51 PM

The Conversion of my 86 Crown Supercoach
Tonight I will speak to the problems found in air system of my Crown:

Symptoms found in the air system of the Crown were:
1) Slow buildup of air pressure.
2) Overnite leakdown of all air pressure
3) The bus would be level after use, but one side slumped down the next day.
(loss of pressure on one side of the air ride suspension)
4) A slight hissing noise under the front left area of the bus.
5) problems maintaining air pressure.

Fixing the problems:
Problem 4 was traced to a slow venting of pressure from the air dryer.
Problem 5 was traced to not one but two different bad governors.
Problem 3 was traced to an intermittently failing check valve
Problem 1 seems to be somewhat lessened by addressing problems 3, 4, and 5.
Problem 2 is also lessened but one more valve is still leaking. The next day 10 psig will be found in the air system. I consider at a minimum that 50 - 65 psig would be acceptable the next day.

I had what I thought was an acceptable level of understanding of how air systems work, but the Crown let me know I needed to learn more.
For those with air system in there bus, Bendix has an excellent tutorial on air systems at:

Of note Cal Fire considers 65 psig present the next day in the air system to be acceptable (for older fire appuratus).

My next post will address the first part of the conversion of my Crown, installation of the Onan 6.5 DKD RV generator.

Iceni John 08-24-2020 01:57 AM

Hi, fellow Crownaholic,

You mention wanting to use flexible solar panels. My suggestion (for what it's worth) - don't! They simply won't last very long: how long's their warranty, compared with regular panels' 25-year warranties? You also need an air gap under the panels, otherwise they'll get so hot that their power output will be seriously affected. I suggest you do some more research on PV panels before you plunk down your hard-earned cash for them: the Northern Arizona Wind & Sun forum has plenty of good reliable info for anyone to learn from.

FYI, I have a smidgeon over 2kW of individually-tiltable panels on my Crown, and still space for two solar water-heating panels whenever I finish building the damn interior! PM me if you need any pointers on how I've done mine - they're very swish!


flattracker 08-24-2020 01:41 PM

The Conversion of my 86 Crown Supercoach
8 Attachment(s)
In this post I document the process of installing an Onan 6.5 DKD diesel generator in the Crown:

I happened upon the opportunity to purchase the generator from a wrecked Bounder 35 ft? motor home from a friend and neighbor down the road. Of course as part of the deal, I had to remove it from the motor home.
It was configured with two 120 VAC output circuits, one with a 30 AMP breaker and the other a 20 AMP breaker.
Once my brother and I removed it from the Bounder, and transported it to the bus, we started it up, using a 1 gallon fuel can and a hose. Sure enough it put out the expected voltages, but not in the configuration I wanted, which is 240 VAC, like the power coming into your RV at a park or to your house.
I found the Onan manuals for this generator on-line and through careful analysis of the schematic determined what wires to change and where to. Onan provides the schematic for the 240 VAC configuration but the labeling of the schematic is confusing. A look in the control box helps some by looking on the inside of the cover at the diagrams. A look at the actual wiring is not the clearest way to understand the changes (see picture). Fortunately Onan does label the important wires so that one can figure out which wire is which. After configuring all wiring out and changing the needed wiring (in the process finding a serious factory defect, a wire to one of the circuit breakers not tightened with obvious heat damage), we started up the generator and checked the voltages and all was good.

Of note, in the model Onan used two seperate breakers for output, different from each other. Other versions of this generator used a dual 30 amp breaker. When researching a replacement dual breaker from Onan it was listed as obsolete not available, but Onan used breakers made by Airpax. A quick trip to eBay and I had the right breaker on the way. The breaker needed has 1/4-20 studs and does not plug into a panel. If you go to an normal electrical supplier looking for a breaker like this they will likely look puzzled and say they don't have them. A marine store or boat store will likely have them as this style of breaker is used on boats.

Based on successful results with my first Crown, I determined that the spare tire compartment was the best place to put the generator on this bus. There is plenty of room in there with excellent airflow so it lends itself to this purpose. In the first bus my son made me a mounting tray and mounted the tray on slides and all fit nicely in the bus, but this generator is taller the the gas engine version of 6.5 Kw Onan in the old bus so a different solution was needed.

We started by removing the spare tire by unscrewing the bolts holding down and removing the tire and wheel. On most crowns there is a substantial U shaped steel support welded to the frame that acts as a cradle to support another substantial steel piece welded to it and the re-enforced horizontal outside body part at the bottom of the access hatch. (see picture).

We cut the welds and removed the steel piece connecting the U shaped support and the outside body support framing (the spare tire mounted to this piece) (see picture)

After cleaning off any rust or undercoating so the surfaces would be ready for welding, and temporarily removing the dump valves (air system) from the body support, we were ready for adding the new generator mounts. Like the first Crown I determined that the generator needed its own fuel tank with a filler in the compartment

First two 4"x1.5" C channel lengths of steel were welded from the U shaped frame welded to the frame rails to the outside frameworks at the hatch opening. (see picture)

Second two more C channel lengths of the same material used in the first two were added inboard on the other side of the U shaped support, with a cross piece at the end of those C channels, and a vertical piece tying the end to the support for the radiator ducting. (see picture) The lengths of C channel on either side of the U shaped support were tied together with additional steel plates on top. To some this may seem overkill but the generator weighs 515 lbs. and a 20 gallon fuel tank full of diesel has about 140 lbs of diesel in it. When you encounter pot holes or bumps (especially speed bumps) the resulting forces could make the approximately 650 lbs. load in the compartment seem to weigh over 1000-1200 lbs., so build your mounts accordingly.

The fuel tank was installed next on the inboard supports. Because the fuel tank's sump stuck down 1.5" below the rest of the tank special considerations had to be taken. The fuel tank requires support under all of it and can not support all of its weight on the four mounting points (it was made for use in a race car), a wood mount was constructed out of some OSB I had in the garage. To make it tall enough we used three layers and saturated the outside with clear polyurethane to seal them up.

The filler system was added next. The tanks filler was about the middle of the top, and consisted of a large circular opening that a flange was mounted to. Two inch exhaust pipe was used for the filler, with diesel certified hose with 90 degree turns where the filler needed to turn. It is important to use the correct hose for this. Do not use radiator hose. An old filler from a junked Dodge pickup was used for the filler and a vented cap topped it off. (see picture)

Of note: before the fuel system was added all of the added support framing was painted with Cummins beige paint. The exhaust pipe is plated for corrosion resistance. To be installed later is a fuel transfer system that will connect to the output of the engine's fuel pump through a solenoid valve and a small fuel pump. The fuel transfer system will monitor how full the generator fuel tank is and stop transfer automatically when the generator fuel tank is near full, and will also stop transfer if the main fuel tank get below 1/3 full.

The actual generator install was a challenge, as the generator is taller than the hatch opening to the compartment. Ultimately we had to remove the cooling system from the generator as well as the mounting cradle. It took all day to install it and get the mounting cradle back underneath the generator. The distance from the mountings we installed and the floor of the bus was sufficient to meet the Onan distance requirements listed in the installation manual. (see pictures).

The exhaust system was some effort, as I didn't want the muffler hanging below the generator and reducing ground clearance. On factor that must be considered is that the generator is on stiff rubber mounts. For my plan to work the muffler had to be mounted the part of the body framework. You do not use rigid connections that connect a fixed mounted piece to a rubber mounted piece. The exhaust pipe now goes forward instead of down, but not too long a distance before turning towards the outside of the bus and connecting to the muffler rigid mounted to the bus body, through flexible exhaust pipe brazed to short lengths of 2" NPT pipe. It is flexible enough to handle any movement between the rigid pipe from the engine to the muffler. (see picture)

After re-installing the cooling system, servicing it, connecting up the fuel system, connecting the generator to 12 VDC (at the alternator), I started up the generator which ran for a couple minutes and quit from fuel starvation, I had another problem to solve.

Reading the service manual was very useful as it contains troubleshooting trees. I determined the the generators engine protection mechanisms were not shutting it down, and the fuel control solenoid only released after it stopped, I noticed I didn't hear the fuel pump. Connecting the fuel pump to 12 VDC showed it did not work any more. These days Auto parts stores don't carry the old style pumps like the Onan had, but I was able to find a usable diesel rated low pressure pump at an AutoZone. The pump needed to have NPT fitting at both ends. The one I bought fit perfectly and I was able to use the Onan hard lines without modifications.

Now the generator was running and producing power (see picture)

In the next post I will talk about the electrical connections from the generator

flattracker 08-24-2020 02:00 PM

Hi John,
I appreciate your advice on the solar panels. I bought the flexible solar panels last fall, 10 total. One major consideration I had was how the bus would look with solar panels on the roof, and the flexible ones have the least impact on the shape and look of the bus. I believe I have a solution for the heat problem. You know these political campaign signs we see every election? They are basically a plastic form of cardboard type material. After the election they have no use, but sandwiched between the panel and the roof they actually would allow airflow between the panel and the roof, as well as insulation.

Iceni John 08-24-2020 03:53 PM


Originally Posted by flattracker (Post 402255)
Hi John,
I appreciate your advice on the solar panels. I bought the flexible solar panels last fall, 10 total. One major consideration I had was how the bus would look with solar panels on the roof, and the flexible ones have the least impact on the shape and look of the bus. I believe I have a solution for the heat problem. You know these political campaign signs we see every election? They are basically a plastic form of cardboard type material. After the election they have no use, but sandwiched between the panel and the roof they actually would allow airflow between the panel and the roof, as well as insulation.

The important thing is to allow a free flow of air under the panels, even when parked - PV thermal deratings make a big difference to power output in hot weather, and with only a thousand watts you don't want to waste any potential power at all. Just a few inches of air gap should work well, in effect making a tropical double-skin roof like old Land Rovers had, and like the MC5 buses that were used by Aramco in Saudi Arabia (complete with extra rear doors for the women!). In hot weather my PV panels, and the central walkway to which they are hinged, are shielding my roof from almost all direct radiant heat, making the bus's interior noticeably cooler because the roof itself is at little more than ambient air temperature. At some point you have to decide what's more important - aesthetics, or functionality and efficiency. Le Corbusier said that a house is simply a machine for living in, so by that same notion a converted bus is also still just a house machine, albeit a mobile one - I generally gravitate towards functionality as the primary determinant of design, but that's just me!

Also bear in mind that the panels, if matching the very arched Crown roof contour, will make the half of them on the lee side produce very little or no power in the winter when the sun is lower and their angle is approaching perpendicular to the sun, or even partially shaded by the curve of the roof. Partially-shaded PV panels produce very little usable power if any at all, so by effectively blocking half the panels' insolation you'll be down to probably only a few hundred watts at best from a nominal 1kW of panels. That's why my panels can be raised up to 21, 33 or 45 degrees from horizontal, to maximize solar harvest even in the winter at higher latitudes during shorter winter daylight. And if half your panels are producing significantly less power than the other half, then you'll need two separate MPPT charge controllers because if you feed differing inputs into one MPPT CC its MPPT function will get mightily confused, resulting in less usable power reaching the batteries. That's partially why I have two Morningstar TS-MPPT-60s, one for each array of panels, so it doesn't matter if the arrays are producing different power. Can't waste those photons!


flattracker 08-24-2020 04:55 PM

Hi John,
Reading your post prompted me to look at the panels that I have. I measured them and found all of them would use up 30 feet front to back on the roof of my bus, they are only about 27 inches wide so they would only cover the center part of the roof of a crown, where there isn't that much curvature to worry about. the plastic campaign signs are still a good bet for insulating the roof from the panels. I plan to try placing one on the bus in the next couple days to see how it would look. I know the rigid panels get warm also, based on temperature measurement I took last winter. I have one of my panels that were damaged rejects from a local solar plant project I got a few years ago. I read 100 degrees in the sun when outside temp was about 40 degrees. I don't think I will actually get the full kilowatt most of the time, but the bus will have multiple power sources. I have calculated my expected power usage and I know I won't be using a whole kilowatt most of the time. My biggest power consumption will occur when running both furnaces and the refrigerator, but none of these are constant power users. Your points are valid though. By the way, I have a second 250 amp alternator mounted on the engine, so when I am driving, that is up to about 2 Kw (only when load is sufficient to cause 250 amp draw)
Thanks though

flattracker 08-29-2020 06:28 PM

1 Attachment(s)
Hi again John,
Today I brought one of my flexible solar panels to the bus for a fit check. I found that when the panel was placed with the longer dimension front to back the curvature is negligible as far as sun angle. When placed with the longer dimension side to side it's still not a major concern. My brother told me that he could not see the panel place on the roof when standing on the ground. I plan to connect the panel to a charge controller and a battery to produce a load, and then monitor the temperature of the panel under load with good sublight. I will let you know of the results. Your input gives me interest to know all operating results of the panels. I will try to add a picture of the panel.
Thanks again

DWJoyce 08-29-2020 10:58 PM

Nice bus.
Let me get this straight. You spent $3000 for the bus, $3700 for a used engine, and $6200 for new gears? Why not just buy a used Prevost? Those things hardly have any wear on them.

Good luck on your project. Have fun and drive safe.

flattracker 08-29-2020 11:53 PM

When I purchased the new Crown it had an engine that ran perfectly. The failure of the main bearing was a complete surprise to me. By then I had purchased many of the items to be installed, as well as fabrication tools, construction materials, etc. My reasoning was either abandon the project, sell a non-running 34 year old bus, and what to do with all the stuff I bought to do the project, or fix the bus. I chose to fix the bus. The gears were an elective modification to improve the usability of the bus, as it had a usable top speed of 63 mph. I now have a roadworthy Crown that will climb any grade and probably get decent fuel economy. I have looked at auctions for Prevost buses and found them expensive to buy, and usually have high mileage.

Bus'n it 08-30-2020 08:48 PM

Its only money. You did the right thing for your needs. I would have done the same. This is why we choose the rigs we choose. If my bus blew its top, well, i would most likely rebuild the engine to a higher spec. Its what we do! Live life. Searching for another is not as fun as it sounds to be. "Run what ya brung!"

Iceni John 08-30-2020 09:13 PM

Regarding solar panel angles for maximum solar harvest, these two websites have useful information:
Optimum Tilt of Solar Panels This is why I have tiltable panels.
Solar Irradiance - calculate the solar energy available on your site You can look up your own home town, or somewhere close to it.

I was also trying to find the NREL's information on insolation values (W/m2) at selected cities around the USA, and how much energy could be expected to be harvested throughout the year at each location depending on whether the panels are fixed or are tiltable in 1-axis or 2-axes. It looks like that site has gone away, but if you can still find it you'll know exactly how much power your own array should produce throughout the year.

Because Bly OR is many hundreds of miles north of sunny Orange County SoCal where I am, it's especially important to design your PV system to harvest as much energy as possible, bearing in mind the much lower sun and shorter daylight hours in the OR winters compared to here.


Iceni John 08-30-2020 09:34 PM

Found it!
Scroll down to page 181 for Medford OR, the closest I could find to your location.


Tejon7 08-31-2020 12:38 AM

Your planning and forethought are inspiring. Bummer about the engine problems, but it sounds like you made the best of it. Having that extra power going up long mountain passes must be awfully nice! I love your bus and I can't wait to read the next chapter in this conversion story. Thanks for sharing.

I feel selfish asking, but... More pictures please! :biggrin:

flattracker 08-31-2020 02:28 AM

The Conversion of my 86 Crown Supercoach
1 Attachment(s)
More pictures are coming!
Thanks for compliments about the bus. My posts will be catching up to the present progress in the next couple days. I hear concern about how much power will be generated from the one Kw array I am installing. I realize that the farther one gets from the equator, the less power can be generated in winter, however it must be a good amount, as there are two large solar plants within one mile of the bus's current location at Bly. The smaller one generates 5 Megawatts and the larger one generates 8 megawatts. Over by the Lake County Airport about 42 miles from Bly is a much much larger plant. I am not too worried about solar generation since I will not be living in the bus, and during the winter I will have more than enough to keep all batteries fully charged.
I also think I did the right thing to repair and upgrade the Crown. Based on my experience of putting over 20,000 miles on my first one, I will enjoy the extra power and highway speed. I believe I could purchase a used factory made motor home for the cost of the Crown and its conversion, I could not match the quality of a Crown Coach for far more cost. An advantage to Skoolies is that ones made after late seventies were made to strict Federal Motor Vehicle Safety Standards (FMVSS) that factory RVs and tour buses were not required to meet. One final point, where else could I ever get the cool lines of a Crown Supercoach? See the remnants of the Crown's original engine.

Native 08-31-2020 03:55 AM

Were you taking it out to the graveyard?

flattracker 08-31-2020 04:02 AM

I have already removed the heads and will be having the sleeves, pistons and rods removed from the block since they are still good, but I planned on scrapping the block since I don't need it. The main bearing is still welded to the crankshaft so it is slated to be yard art. I haven't determined what to do with all the extra parts from the donor engine yet.

flattracker 08-31-2020 04:05 AM

The Conversion of my 86 Crown Supercoach
3 Attachment(s)
In this post I discuss my generator wiring installation along with some illustrations.
In my previous posting I documented that the generator is configured for two legs of 120 VAC/ 240 VAC. To connect this to the RV electrical system I am doing like one would connect to a house, using four wires:

Black - hot 120 VAC
Neutral - for both legs of 120 VAC
Red - hot 120 VAC
Green - Ground

The generator, an Onan 6.5 DKD (6.5 Kw powered by a 3 cylinder Kubota Diesel) is installed in what was the spare tire compartment. It has two 30 Amp legs (even though that equals 7200 watts total Onan rates it at 6500 watts)
To carry 30 amps one needs 10 gauge wire. I went overkill and used 8 gauge wire.
This generator also came with remote operation capability, a feature I want to use. The wrecked motor I removed it from after purchase had a remote start on the instrument panel, but it was just the switch and a light.

Making the remote operation cable:
I studied the manuals for the generator, as well as examined the remote cable that came with the generator, and realized the 9 pin connector on the generator only used 7 of the 9 sockets on its connector. The approximately 5 feet of cable I could extract from the wrecked motor home only used five wires. The cable consisted of the male connector 8 wires, stubbed with the needed ones spliced to wires installed during manufacture of the motor home. I removed all added wires from the stubbed wires, and spliced about 25 feet of new wire to each of the 7 wires actually used. It turns out that oil pressure and coolant temperature gauges are optional on this generator. I wanted both for my installation, so all the wires used are now there.

The installation method:
Between the now generator compartment and the engine compartment is a steel wall, and all wiring to/from the generator has to pass through it. I wanted a way to provide water resistant passage through the bulkhead for the generator's output and controls, so I used outlet boxes made for use outside. These boxes have an opening in the back, ends and sides, and are made to mount to a surface through holes you punch through the casting. I mounted two of these boxes on the firewall in the generator compartment. They can be seen in the attached picture in my posting of the generator install. I used 1/2 " NPT pipe with an adapter to fit the 3/4" hole in the back of the cast outlet box, connected with various conduit components to keep water out (see the picture). The power output wiring from the generator was passed through using 3/4" conduit components (also in the picture) The two conduits pass to the rear of the bus just under the floor, passing through two cross members under the floor, and up through the floor to inside the bus. All total within less than 10" basically inline are three conduits, and one of the Propane lines next to the wall of the bus. (see second picture)
Ten foot lengths of conduit are sufficient to connect at the engine side of the bulkhead to the point where all go through the floor. The through floor location is just before the wheel well. It is a protected location.

The additional hatch:
Because the area to the right of the transmission is the planned location of the holding tank and the propane tank, an additional hatch is necessary for ease of access for installation and usage. I do not want intrusions into the engine compartment and alongside the transmission is unused space. We made an opening through the body siding below the floor the same size and the ones for the engine and the original spare tire compartment. The new hatch is not yet installed but the materials for the new cover are in hand.

The connection for outside power:
I constructed a connector mount to mount underneath the floor adjacent to the second crossmember near the through floor connections. I am using a twist lock 4 pin connector that is standard for 50 Amp service at an RV park. I used 6 gauge wire in a single cable passing through 3/4" NPT pipe. (see third picture) This is the third cable in the row of electrical wiring through the floor.

In the next post I will discuss the fabrication of the holding tank frames and mounts, the installation of the propane tank, and the holding tank. I will also discuss the installation of part of the propane plumbing.

JackE 08-31-2020 06:26 PM


Originally Posted by flattracker (Post 402251)
It was configured with two 120 VAC output circuits, one with a 30 AMP breaker and the other a 20 AMP breaker.
Once my brother and I removed it from the Bounder, and transported it to the bus, we started it up, using a 1 gallon fuel can and a hose. Sure enough it put out the expected voltages, but not in the configuration I wanted, which is 240 VAC, like the power coming into your RV at a park or to your house.
I found the Onan manuals for this generator on-line and through careful analysis of the schematic determined what wires to change and where to. Onan provides the schematic for the 240 VAC configuration but the labeling of the schematic is confusing. A look in the control box helps some by looking on the inside of the cover at the diagrams. A look at the actual wiring is not the clearest way to understand the changes (see picture). Fortunately Onan does label the important wires so that one can figure out which wire is which. After configuring all wiring out and changing the needed wiring (in the process finding a serious factory defect, a wire to one of the circuit breakers not tightened with obvious heat damage), we started up the generator and checked the voltages and all was good.

I'm curious about being able to switch this from a 120 to a 240 application. I have a 6500 watt onan out of a Southwind. It is a 2 cylinder gas variety. Is there a possibility this has the same capability of being switched to a 240V generator? Mine has 2 separate 120 legs and breakers in the generator body that are labeled 15 amps each. I know just enough about electricity to let go when I'm getting shocked.....:nonono: Actually I do understand quite a bit about it, but not enough to know this was even a possibility. I have already mounted the genny under the bus, but since I did that, I decided to buy a 12,000 watt 240V to replace it with. If I can convert this one, I can leave it where it is and can dedicate the new one to running the house during our frequent power outages.

flattracker 08-31-2020 11:33 PM

configuration of 2 cylinder onan gas powered 6.5 Kw generator
You don't state which model of Onan generator so I cannot give the most definitive answer. However for older models of 2 cylinder gas powered generators the following may help:
If you generator has all its covers still installed, there will be a schematic and wiring diagrams found inside the cover. The 5 Kw Onan I have in the collection has four wires labeled M1 through M4 inside the cover. On this generator, there are three possible wiring/voltage output configurations:

A) 240 VAC with neutral - M2, M3 connected together for neutral and ground.
M1 hot 120 VAC to neutral (M2)
M4 hot 120 VAC to neutral (M2)
M1 - M4 240 VAC

B) 240 VAC - M1, M4 connected together
M2, M4 240 VAC M2 is ground

C) 120 VAC - M1, M3 connected
M2, M4 connected
M1, M4 120VAC ground at M2
The 6.5 Kw should be the same if it is of similar vintage. The later Emerald series I have not looked at

84chevyguyid 09-01-2020 01:05 AM

Sweet bus! I attached a really good video about bus insulation techniques that may be of interest.

flattracker 09-01-2020 03:48 AM

thank you for the link. I watched the video.

Native 09-01-2020 04:45 AM

You may be interested in his testamonial on the EHP company website.

JackE 09-01-2020 08:37 AM


Originally Posted by flattracker (Post 403599)
You don't state which model of Onan generator so I cannot give the most definitive answer. However for older models of 2 cylinder gas powered generators the following may help:
If you generator has all its covers still installed, there will be a schematic and wiring diagrams found inside the cover. The 5 Kw Onan I have in the collection has four wires labeled M1 through M4 inside the cover. On this generator, there are three possible wiring/voltage output configurations:

A) 240 VAC with neutral - M2, M3 connected together for neutral and ground.
M1 hot 120 VAC to neutral (M2)
M4 hot 120 VAC to neutral (M2)
M1 - M4 240 VAC

B) 240 VAC - M1, M4 connected together
M2, M4 240 VAC M2 is ground

C) 120 VAC - M1, M3 connected
M2, M4 connected
M1, M4 120VAC ground at M2
The 6.5 Kw should be the same if it is of similar vintage. The later Emerald series I have not looked at

Thank you. At least this gives me somewhere to start looking. I have the Emerald III GenSet. I'll check with Mr. Google and see what I can learn.

flattracker 09-09-2020 05:08 AM

The Conversion of my 86 Crown Supercoach
8 Attachment(s)
In this post I discuss the installation of the propane tank, fabrication of the holding tank mounts, and installation of the holding tank under my 86 Crown.

When I did the conversion of the previous Crown, a 1981 two axle 35' model with the Detroit 671 with the optional turbo, my son Perry did some of the fabrication and welding to mount the tank, fastened to two cross member between the frame rails and the outer body framework. This worked very well and I decided to replicate that setup again.
There are a couple differences between the two installations, first being that we bolted the inner mounting brackets to the cross members instead of welding to them, and second, the drain end is towards the front instead of to the rear. Bolting the support brackets to the cross members was done so that all of the tank mounts could be removed if needed to work on the transmission of the bus. Placing the drain end forward makes it easier to operate the gate valve and connect the waste hose to the tank.

Before any of the effort to install the outside power connections, the holding tank and the propane tank, it was necessary to make the opening for a third right side hatch like the two already there. We started by drilling holes for each of the corners, to later use a hole saw to make the corners. Using a hole saw all four corners were cut. Using a hand grinder with a cutting wheel, all of the sides of the opening were cut. Being aluminum it wasn't too bad to do the cutting, although using the battery powered grinder made for quickly dead batteries. The opening edges were cleaned up using a hand grinder and later a file.

The mounts consist of two rectangular frames made from 1" x 1" x .120 steel, two inner brackets that connect the tank mounts to the cross-members and two outer mount points that secure the framework to the frame of the outer body of the Crown.

First the two rectangular frames were cut with 45 degree angles for the corners. Both frames are sized to the outer dimensions of the mounting flange of the tank. The two frames were the same size and to be mounted one below and one above the mounting flange of the tank. (see photos)

Since the bus is located in a storage yard on a concrete pad about six miles from the house, after MIG welding them together at the corners and grinding the welds a little, we brought them to the house and match drilled them with 5/16" holes using a vertical mill with a digital readout. After bringing them back to the bus we then placed the tank in between the frames and match drilled the tank's flange to the frames. (the mill was used because drilling the holes by hand with a hand electric drill would take forever)

(see photos)

For one half of the outer mounts, steel plates were cut and MIG welded to the lower frame that goes under the flange. The tank and frames were temporarily assembled.

Using a motorcycle jack and wood blocks, the tank and frames were positioned under the bus as close as we could to the intended position, for placement of the outer mounts. The mounting plates were match drilled to the tank's lower frame and temporarily bolted together.

Having satisfied ourselves that the tank was placed how and where we wanted it (we is my brother and I), I tack welded the outer mounting brackets to the side body framework of the Crown. We removed the frames from under the bus to weld the outer mounts the rest of the way. Before any welding was done, the outer body framework was prepped for welding by using a hand grinder with a flapwheel to remove the undercoating and provide a clean surface. Brakeclean was also used to complete surface prep. The steel plates used for the mounts was also touched up with the flapwheel and more Brakeclean. The outer mounts were then MIG welded in place. The outer body framework is thick enough to weld on using a MIG welder.
(see pictures)

Two inner mounts were fabricated, sizing there component parts for length and placement using the tank frames and clamping the various pieces where they were to be used. The inner mount brackets were fabricated using 1" x 2" x .120 steel, and 1/8" steel plate.

Even through the steel used for the inner mounting brackets is new, we still touched the areas to be welded with a flapwheel and Brakeclean. Both the inner mounting brackets are different from each other as the rearmost edge of the tank frame almost lines up to the rear cross-member and the front is some distance back from the front cross-member. With the pieces cut using a band saw and clamped in a vice, I welded all of the pieces together for each mount bracket. Since the front inner mounting bracket requires a 90 degree turn, the connected was gusseted for strength.

With all parts for the tank mounts fabricated, all were thoroughly cleaned with Brakeclean and painted with white Rustolium rattle can paint. The inner mount brackets were installed to the cross members. Note: we matched drilled the brackets to the cross-members and took extra precautions for the hoses and wiring mounted to the forward side of the front cross-member so as to not drill through them and cause ourselves much grief.
(see pictures)

The bolt holes where the inner mounting brackets connect to the tank's frames were match drilled. A total of two additional mounting bolt holes were match drilled in the outer mounts for additional strength.

I realize that some may think that I am over engineering this tank mount but remember how much weight can be inside the holding tank (7lbs x 40 gallons = 280 lbs + the weight of the tank and frames and brackets)

After all of this we removed the tank and frames again, to install the propane tank. The inner tanks mounting brackets were left installed as they clear the propane tank.

The propane tank holds about 24 gallons of propane, being empty it wasn't too heavy.

The propane tank has two outside mount points on its top and two inside mounts to fasten it to a bulkhead or wall in back. Since we are mounting it to the floor of the bus, two mounting brackets bolt to the tank's wall mount tabs and provide two mount points facing up to the floor.

After cleanup of the outside of the tank and application of more Rustolium rattle can paint to it. We jacked it into position using the motorcycle jack and wood blocks. After adjusting the tank's position to where we wanted it, we used the Rustolium paint to spray four markers onto the bottom side of the Crown floor. After removal of the tank we drilled four holes through the floor to mount the tank. We then jacked up the tank into position and installed four through hole bolts and two nuts (with washers) (the outer tank mounts have large nut plates welded in place)
With everything tightened up, the propane tank was mounted. (see pictures)

We next assembled the upper and lower mounting frames to the holding tank, placed it under the bus, raising the inner side into the inner mounting brackets and pulled the tank and frames into place to bolt the outer mounts together. The bolts were installed but not tightened, to allow for adjustments. The inner mount bolts were installed, and all bolts tightened up. The Holding tank is now installed. (see pictures)

The first drain plumbing:
With the holding tank in place, it was time to install the drain plumbing for the toilet.
RV toilets are different than house toilets in a couple respects:
1) They are designed for a low pressure water supply.
2) They do not have the trap like a house toilet, but a a straight shot down the hole.

Because of this one should plumb RV toilets with as little resistance to good flow, as possible. Placement of the toilet is based on clearance from planned walls for the "water closet" and distance from the bathroom sink.

This I had planned out during the cold months and had designed the layout of the Water Closet. Following my guidelines from the design exercise, and the installation instructions, I marked X marks the spot and, using the hole saw, made a large hole through the floor of the Crown. For those dying to know, the wood floor of a Crown is three layers of wood, with the upper and lowest layers in plywood, and the middle "pressed sawdust". There is also a 1/8" thick layer of rubber flooring glued on top. The pictures show that under the floor on the right side of the bus along side the transmission is starting to look kind of busy, but almost all of the installations underfloor are done. The total thickness is 1 1/2". The three layers of wood are not glued together.

The plumbing parts picked were a matter of trial and error figuring out from the pile of parts picked up at Home Depot and Diamond Home improvement. The goals were twofold, the least resistance to flow, and a match-up at the toilet flange and the top of the holding tank.

The parts for the drain pipe were assembled with the glue (actually a mix of dissolved ABS plastic and solvent). The location for the 3" flange was determined, and hole cut with the hole saw. The flange was glued in place and connected to the plumbing through a rubber coupling with two hose clamps. Remember it is important in your design to make all tanks and such removable at a later time. This was done with the first Crown and worked well with no leaks.
(see pictures)

The next post covers the installation of the new hatch cover.

flattracker 09-09-2020 05:24 AM

The Conversion of my 86 Crown Supercoach
4 Attachment(s)
Here are some additional photos

flattracker 09-14-2020 04:03 AM

The Conversion of my 86 Crown Supercoach
5 Attachment(s)
This is another post in my conversion of my 1986 Crown Supercoach. In this post I document the effort to fabricate and install a new hatch to cover the opening we made to provide access to the Propane tank, external power connection, and external water connection to the bus.

I made the decision to not obstruct access to the engine, and also install the holding tank, and propane tank so that they could be removed for access to the transmission if repair is ever needed.

I designed the conversion so that when outside power, water and sewer are connected, that the access cover could be closed and one would not see these connections.

To that end we cut and opening that is the same size as the ones for the spare tire bay, and the engine bay.

We measured the existing hatch for the engine bay and found that it is 48" x 24" x .100". Aluminum is available in .100" thickness, but where I live one has to purchase an entire 4' x 8' sheet. The metal is special order here,and I ordered the whole sheet, and requested two pieces be cut from the sheet, one being 24" x 48", and a second 48" x 5 1/4". The metal was cut in a shear, and the resulting pieces delivered to the storage yard where I keep the bus.

I also ordered a piano hinge 3" wide, stainless steel, 1/4" thick pin. I also requested that it have a 270 degree range, from closed to fully open. I could only order the hinge in 72" lengths. I got the hinge from Fastenall.

Next came the work to bend the hinge to the profile used by Crown. I went to all the places in Klamath FalIs that have a sheet metal brake, and none could duplicate the profile used by Crown for that piece. This piece is where crown mounted the latches to hold the hatch closed. Ultimately I went to a friend at the Airport at Lakeview, Or. who has a 4' wide sheetmetal brake and was willing to let me use it to bend the aluminum. The Crown hatches have a piece of aluminum mounted at the lower edge, and we tried to duplicate that. What we found was that we could bend all but the last bend, as the metal we were attempting to bend got in the way. WE did make the first three bends. The piano hinge requires two bends, and we were able to make those. Our bends were not as crisp as the one made by crown, but the results were usable.
I drilled 5 holes through the stainless steel hinge, and then match drilled holes in the aluminum plate. (see pictures)

I riveted the hinge to the aluminum plate using 1/4" pop rivets. (see pictures)
I drilled holes through the hinge in preparation to mounting the new hatch to the bus.

Using Gorilla tape, I temp mounted the hatch to the side of the bus in order to match drill mounting holes in the bus. I drilled the center hole first and temporarily installed a 1/4 - 20 bolt and nut to hold the hatch in place. This makes it easier to match the outer holes and fasten them later. Ultimately I match drilled a number of holes through the hinge and the bus body, while keeping the hatch as close a position match as the ones Crown installed. For the time being the hinge is bolted to the bus body.
Now having the hatch attached to the bus, next came the mounts for the Crown latches. In my case I still had an original Crown hatch from the parts bus of years ago. I did not re-use the hatch from the 73 Crown parts bus because the hatches from that bus are smaller in length and height. I decided that it wasn't necessary for the latch mounting bracket we bent to run the full length of the hatch (actually near full length).
I cut two lengths of the bracket at 5 1/2" long. I then cut the extra metal from the bracket, checked fit. All would fit the way I had hoped.

I drilled two holes about 1/2" from the lower edge of the panel and match drilled two holes in each latch mount bracket. After pop riveting both brackets, fitting the original Crown latches was next. On the original hatch from 1973, the latch assembly was screwed to the aluminum panel with genuine "Crown screws", so those were unscrewed. Placing the hinge on the upper ledge of the mounting brackets (when the hatch is opened), allowed perfect alignment with the metal ledge of the lower body framework. I marked the location of the latch and its mounting holes, and subsequently drilled the mounting holes through the mounting bracket. After temporarily bolting the latch to the bracket, I drilled a pilot hole through the bracket and the hatch using the square hole through the latch. After removing the latch, 1/2" holes were drilled through both the bracket, and hatch panel. I again bolted the latch to the mounting bracket using two washers just like Crown did originally. I then performed a fit check to latch the hatch. It worked but needed additional mounting so a 5 1/2" length of of 1 /1/2" aluminum angle metal was added to the lower side (with hatch open) of the mounting bracket. This connected the unconnected side of the bracket to the hatch to the panel. (see picture)

The same operations were performed on the second mount and latch. A fit check was performed latching both ends of the hatch, and all worked quite well. Two extra rivets were added between the mounting bracket and the hatch panel for strength.

The hatch now closes and latches just right. (see picture) One last step is mounting the chain that connects between the hatch panel and the ring mounted to the side of the bus. The original hatch panel still had the chain attached so I removed it from the original panel and match drilled two mounting holes through the new hatch panel, and attached the chain. The chain from the old hatch panel was right at twice as long as the ones on the later Crowns so I shortened it. All thats left is fabrication of a body mounted ring to hook the chain on to provide a means to hold the hatch open when needed.

At this point, after fabrication and installation of the retaining ring I am about as far as I can go under the bus before I install some unistrut inside to frame up walls.

Yes I did say Unistrut. When I converted the previous Crown I used Unistrut to frame up walls and counters. This worked very well. I am more comfortable cutting and welding steel than I am doing woodworking. Plus it is very strong, doesn't squeak going down the road, and there is every kind of imaginable bracket made to mount things to unistrut. Once the plating is removed using a grinder, it is easily welded.

My next task is to re-produce the template I made and used to cut the Unistrut to fit inside the Crowns body. I will detail how I do that in my next posting.

flattracker 10-19-2020 10:09 PM

The conversion of my 86 Crown Supercoach
1 Attachment(s)
In my previous post I mentioned I would post about making a template for cutting the unistrut to be used in construction of the walls in the interior of the bus. To that end I came up with an approach to capture the profile I needed to cut when matching the strut to the sides of the interior. The first picture is of what I did on my first conversion of the 1981 Crown. As one can see the Unistrut is mounted against the side of the bus

flattracker 10-19-2020 10:21 PM

The conversion of my 86 Crown Supercoach
2 Attachment(s)
I do not still have the template that I used in the previous conversion, so I needed to produce another. I concluded that the tools with the thin metal fingers held in a row and made to capture the profile of moldings and such would work, but found that the ones I could find locally were made to capture just six inches of profile. My solution was to attach two of them to a piece of steel strap so I could capture almost 12 inches in length. In the second and third pictures I show the details of the tool.

flattracker 10-19-2020 10:29 PM

The Conversion of my 86 Crown Supercoach
1 Attachment(s)
I captured the profile I needed, ultimately needing to move the tool lower to get the lowest parts of the profile. Each capture was traced into foam/cardboard poster board.

Afterwards I cut the resulting template out, and after making minor adjustments, trimming the template I produced the template shown in the last picture.
I will transfer this template to a sheet of aluminum to produce a durable one.

flattracker 10-19-2020 10:32 PM

The Conversion of my 86 Crown Supercoach
My next post documents the production and installation of two air conditioner plenums on the roof of the Crown.

flattracker 10-19-2020 11:01 PM

The Conversion of my 86 Crown Supercoach
1 Attachment(s)
This post documents the production and installation of air conditioner plenums through the roof of the Crown bus. The Crown bus has a very strong roof, supported by high strength steel ribs. The ceiling has an inside layer of aluminum about 60 thousands thick, riveted on one inch centers to steel ribs that cover side to side as well as additional ribs that go front to back. On top is another 60 thousands thick layer of aluminum riveted to the ribs on one inch centers.

A 250 lb person will not dent the roof.

The problem with the Crown's roof is that it is curved more than the usual motor home or other RV. I have not looked close at any other brands of skoolie to see what level of curvature they are so I cannot say about them.

But, given the curvature of the Crown's roof and the fact that RV air conditioners are flat on the bottom, this creates a need to address this.

I was left with almost a 4' x 6' piece of aluminum sheet 100 thousands thick. This provided the raw materials for the plenums.

Since the air conditioners were designed for the 14" x 14" openings the plenums needed to provide that.
Using the low cost Harbor Freight hand grinders with cutting wheels was a good way to cut out the top part of the plenums. With practice one can cut reasonably straight lines in aluminum, using multiple passes. Inside corners can be finished using a hack saw blade. Being unsure how tall the plenum actually needed to be we cut them taller than we expected them to be. Removing metal is much easier than adding metal.
The outside dimension of the plenums was made larger than needed also.
The first picture shows a plenum after taping the pieces together for mockup.

flattracker 10-19-2020 11:18 PM

The Conversion of my 86 Crown Supercoach
2 Attachment(s)
Being the plenums are made of aluminum they were welded using the TIG process. I need some practice using TIG so I brought the job to my son Perry, as he has a TIG welder and has done it more than I have.

He started out the welding by tack welding the pieces together. By welding only small beads to start out, it minimizes distortions due to expansion from the heat of welding.

He welded both plenums with beads a couple inches at a time. Distortion was kept to a minimum.

In the next picture, the short tack welds are visible on the outside of the sides of the plenum, while the full length beads are visible on the inside.

In the second picture both plenums are shown.

flattracker 10-19-2020 11:42 PM

The Conversion of my 86 Crown Supercoach
2 Attachment(s)
Installation of the plenums required cutting square holes through the roof of the Crown.
Once again, I produced a template, this time out of cardboard, with a 14" x 14" opening cut in it. Using a tape measure, we found the centerline of the bus (which has a line of rivets down it) and using the template drew the square on the roof using a sharpie. This process was repeated for the front opening location on the bus.

The first picture shows one of the openings.

The second picture shows the template and the marked location for the opening.

flattracker 10-20-2020 12:00 AM

The Conversion of my 86 Crown Supercoach
2 Attachment(s)
Because we had cut the openings in the Crown's roof a little undersize, the openings had to be fitted to the plenums. More work with the low priced hand grinder accomplished this and the plenums now fit through the openings well. The two openings, while the same size, where placed differently in relation to the supporting rib in the roof. The rear one had a rib going accross the middle of the opening, while the front one we placed between two ribs. We ended up removing a small amount of each rib in the front one and removed a portion of the one rib passing through the rear one.

To the rib passing through the rear one we added brackets to attach the plenum to, to secure the plenum to the bus. A large amount of silicone caulk was added to the underside of the plenum in the rear and then the plenum installed into the opening. A tool box full of tools was placed on top for weight. The next day the air conditioner was placed on the plenum and bolted down.
The securing of the plenum get finished tomorrow.

flattracker 10-20-2020 03:02 AM

The Conversion of my 86 Crown Supercoach
1 Attachment(s)
Another picture of one of the plenums set into the opening in the Crown's roof. In this image it is easy to see the curvature of the roof compared to the flat plenum.

flattracker 10-29-2020 03:33 AM

The Conversion of my 86 Crown Supercoach
3 Attachment(s)
An update on the conversion of my 1986 Crown:
air conditioners are now mounted to the roof of the bus. I have some pictures of the results.

The pictures show the mounted and covered units on the bus.

flattracker 10-29-2020 04:01 AM

The Conversion of my 86 Crown Supercoach
Today I took the Crown out for a drive. I needed to see how everything done so far would work going down the road. I left the storage yard at Bly, headed for Lakeview, about 42 miles from Bly, in the next county. I mounted the GPS on the windshield so that I would have a good read on my actual speed. The route I used is on Oregon hwy 140. This stretch of highway is a two lane back road with moderate curves and some hills to climb. The highest elevation is about 5100 feet. Bly is about 4300 ft elevation.
With the cold weather we are having the bus does not like to start cold as the Cummins Big Cam engine does not have glow plugs. I had a new engine block heater installed on the replacement Cummins engine. I started out by plugging the block heater into the temporary electrical box, starting up the generator (which has glow plugs) and running it for awhile. While waiting for engine block warmup, I filled the one low tire on the bus. Once the block was warmed, the bus started fine. This is my first time out with the new engine and taller gearing with a gps so that I really knew my speed. The first thing I discovered was how easy 70 mph was to reach. Considering the elevation, and the fact the Big Cam engine in the bus is strictly mechanical, I was a little surprised. When the speed was about 50 mph, the bus was a little doggy, with an estimated rpm about 1500 (haven't replaced the tach yet), but when going at least 60, additional speed was easier. I had to keep an eye on the speed because several times the bus got to 70 mph and I don't want attention from the State troopers. (yes they were there) The trip was uneventful. There were no squeaks from the air conditioner mounts. Some parts of this stretch of highway are real bumpy, with some vehicles worse than others and the Crown did not like the bumpy parts. I'm now thinking that maybe front shocks would be in order. Other than the bouncy ride I was very satisfied with the performance. I think open highway and freeway performance will be more than adequate. I decided that next on the list is installation of the new tachometer. By the way, ISSPRO still has tachometers in stock for Crowns. My Crown has the pulse generator driven by the fuel pump via cable, and they also still stock the pulse generator used with that setup. I will post the results of the tach installation next.

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